1. Field of the Invention.
This invention relates generally to intra-channel clarifiers and, more particularly, to devices which control the fluid dynamics of sewage stream circulating around the clarifier.
2. Prior Art.
In oxidation ditch sewage treatment systems, intra-channel clarifiers are often employed. Examples of intrachannel clarifiers may be seen in Harold J. Beard's U.S. Pat. Nos. 4,362,625; 4,383,922; and 4,457,844. Such clarifiers function by utilizing the hydraulic head losses created by a moving stream of sewage as it passes around and/or under a stationary semi-submerged structure.
The channel itself may be a round or oval tank, usually with a central partition forming a continuous channel in which to circulate a sewage stream. In the conventional system, the waste water is constantly flowed in the ditch while at the same time aerated to provide oxygen for microorganisms decomposing the sewage. A clarifier having side walls, a bottom and a number of sludge removal ports in the bottom can be positioned in the sewage stream within the channel. Pressure differences between the interior and the exterior of the clarifier cause the circulating sewage to be drawn within the clarifier where reduced velocities promote separation of sediment and sludge from the waste water. Sludge is withdrawn from the bottom of the clarifier through a series of sludge removal ports of some type and the clarified liquid is then removed from the interior of the clarifier. The velocity of the waste stream flowing beneath the bottom of the clarifier creates a pressure differential and draws sludge out of the clarifier and back into the stream where it is digested further.
One of the methods of controlling the head differential created by the waste water stream flowing beneath the clarifier has been to raise or lower the clarifier within the channel. By varying the displacement of the clarifier, the velocity of the waste stream past the sludge removal ports can be varied thereby varying the rate of sludge removal from the clarifier. However, the sheer bulk of the clarifier makes this method of adjustment awkward. An improved method of adjusting the fluid dynamics of the waste water stream flowing past the clarifier is desired.